1. Technical Field
This invention relates to parts of an internal combustion engine or the like and, more particularly, to apparatus for ducting the exhaust emissions of an internal combustion engine comprising; a plurality of header pipes connected to and receiving exhaust gases from the plurality of the exhaust ports of the engine; and an outlet therefrom connected to an exhaust pipe. More specifically, the invention relates to a breakage resistant, high temperature resistant, corrosion resistant, low heat rejection, structural fiber reinforced ceramic matrix composite exhaust manifold for internal combustion engine applications.
2. Background Art
For many years, the exhaust systems of internal combustion engines have remained substantially unchanged. There is a metal exhaust manifold, typically cast iron or steel, or tubular steel, that collects the exhaust gases emitted from the exhaust ports of the engine and outputs them into a single exhaust pipe. Typically, a muffler, and/or a catalytic converter device is disposed in-line with the exhaust pipe to reduce noise and pollutants associated with engine operation. A typical prior art exhaust manifold design is depicted in simplified form in FIG. 1 where it is generally indicated as 10. There are a plurality of flanges 12 which are bolted or clamped over the exhaust ports (not shown) of the engine (also not shown). The flanges connect individual header pipes 14 to a common outlet pipe 16 which leads and is connected to the exhaust system (not shown) at 18. Since good (minimal restriction) exhaust gas flow is important in overall engine performance, the curves of the pipes, the interior smoothness, and the like, are factors considered by designers thereof. Such factors are somewhat relevant to the novelty of the present invention but will not be addressed herein in favor of simplified drawings which clearly point out the true novelty in a manner easily understood by those of ordinary skill in the art.
Most early and present prior art exhaust manifolds were totally of metal as indicated in FIG. 2. Commercial manifolds were/are generally of cast iron or cast steel while specialty manifolds for high performance engines and the like were/are of welded steel or stainless steel pipe so as to provide a "tuned" exhaust as known to those skilled in the art. Engine designers continue to have difficulties with current exhaust manifolds of metal design in two distinct arenas. First, during heavy load engine operation exhaust gases can be in excess of 1400.degree. F. while the engine block that it is mechanically connected to is held to a maximum of 300.degree. F. by the water cooling system. If a cast iron exhaust manifold is allowed to get too hot, the manifold can warp or even crack due to the large loads introduced into it from the large differences in thermal expansion between the two mechanically connected parts. This is due to its higher temperature. The manifold wants to thermally grow to a much larger size than the mechanical connection to the block will allow. This failure allows raw exhaust gases into the engine compartment. This occurrence typically requires replacement of, or removal and repair of, the manifold. Although this is not a well known problem, those skilled in the art of engine design will agree that it is a continuing dilemma. Current technology approaches to alleviating the problem are to utilizes a much higher cost stainless steel, which has a substantially lower coefficient of thermal expansion than cast iron, or to reduce the overall temperature of the exhaust manifold by increasing the heat rejected back to the block at the mounting flanges, or to segment the exhaust manifold into sections that slide inside one another so as to provide the manifold with the ability to grow. The segmented exhaust manifolds, however, tend to leak at the joints over time. The second major arena of difficulty for engine designers comes primarily in the marine industry. Here, regulatory requirements dictate maximum allowable engine compartment temperatures and engine "touch" temperatures for in-board marine applications. This typically requires the use of water cooled exhaust manifolds to achieve the regulatory constraints. The main problem associated with this approach is corrosion of the metal manifold. As a result, water-cooled cast iron manifolds must be replaced much more often than desirable; or, the manifolds must be manufactured of a much more costly stainless steel material.
More recently, for use with engines having higher operating temperatures, the addition of a ceramic liner 20, as shown in FIG. 3, has been suggested. For this, the prior art suggests only the use of a monolithic ceramic material. See, for example, the 1995 patent of Ford Motor Company to Hartsock (5,404,721).
In another co-pending application entitled METHODS AND APPARATUS FOR MAKING CERAMIC MATRIX COMPOSITE LINED AUTOMOTIVE PARTS AND FIBER REINFORCED CERAMIC MATRIX COMPOSITE AUTOMOTIVE PARTS by the inventors herein Ser. No. 08/515,89, filed on Aug. 16, 1995 and assigned to the common assignee of this application, an improved structural fiber reinforced ceramic matrix composite (FRCMC) material is disclosed for lining metal parts such as exhaust manifolds which does not suffer from the problems of failure due to thermal shock, damage from minor impacts, or erosion of a monolithic ceramic liner, the following is a summary of the above co-pending patent application, the teachings of which are incorporated herein by reference.